Isotopic bromine

The presence of a chlorine or bromine atom results in an intense (M + 2) peak due to the presence of either two chlorine isotopes (chlorine-35 and chlorine-37) or two bromine isotopes (bromine-79 and bromine-81). In the case of chlorine, the (M + 2) peak is about one-third the intensity of the M ... 

Isotopes can help determine the atomic mass (not mass number) of an element. The atomic mass for an element can be found on the periodic table. The atomic mass is a number that contains decimal places. Why Can there be a fraction of a proton or neutron The atomic mass is not a whole number because the atomic mass takes into account all of the masses of the isotopes of an atom and their relative abundance. For example, bromine has two isotopes, bromine-79 and bromine-81. It has been discovered that 50% of all bromine atoms are bromine-79 and 50% are bromine-81. From this you can calculate why the atomic mass of bromine is 80 ... 

Nitrogen has two naturally occurring isotopes nitrogen-14 (mass = 14.00 amu) and nitrogen-15 (mass = 15.00 amu). Bromine also has two naturally occurring isotopes bromine-79 (mass = 78.92 amu) and bromine-81 (mass = 80.92 amu). How many NBr3 molecules of different masses can exist Determine the mass (in amu) of each of them. 

Bromine has two naturally occurring isotopes, bromine-79 and bromine-81, with masses of 78.918338 u and 80.916291 u, respectively. Bromine has an atomic mass interval of [79.901,79.907]. Estimate the percent isotopic abundances of Br by using (a) the lower bound and (b) the upper bound of the atomic mass interval. 

Isotopic clusters are especially apparent when atoms such as bromine and chlorine are present m an organic compound The natural ratios of isotopes m these elements are... 

Compounds that contain chlorine, bromine, sulfur, or silicon are usually apparent from prominent peaks at masses 2, 4, 6, and so on, units larger than the nominal mass of the parent or fragment ion. Eor example, when one chlorine atom is present, the P + 2 mass peak will be about one-third the intensity of the parent peak. When one bromine atom is present, the P + 2 mass peak will be about the same intensity as the parent peak. The abundance of heavy isotopes is treated in terms of the binomial expansion (a -I- h) , where a is the relative abundance of the light isotope, b is the relative abundance of the heavy isotope, and m is the number of atoms of the particular element present in the molecule. If two bromine atoms are present, the binomial expansion is... 

Before sample preparation, surrogate compounds must be added to the matrix. These are used to evaluate the efficiency of recovery of sample for any analytical method. Surrogate standards are often brominated, fluorinated, or isotopically labeled compounds that are not expected to be present in environmental media. If the surrogates are detected by GC/MS within the specified range, it is... 

For other elements that occur with major relative abundances of more than one isotope in the natural state, the isotope pattern becomes much more complex. For example, with chlorine and bromine, the presence of these elements is clearly apparent from the isotopes Cl and for chlorine and Br and Br for bromine. Figure 47.2a shows the molecular ion region for the compound chlorodecane. Now, there are new situations in that C, C, C1, and Cl isotopes all have probabilities of occurring together. Thus, there are molecular ion peaks for + Cl, C + Cl, + Cl, and so on. Even so, the isotopic ratio of 3 1 for Cl to Cl is very clear... 

Partial mass spectra showing the isotope patterns in the molecular ion regions for ions containing carbon and (a) only one chlorine atom, (b) only one bromine atom, and (c) one chlorine and one bromine atom. The isotope patterns are quite different from each other. Note how the halogen isotope ratios appear very clearly as 3 1 for chlorine in (a), 1 1 for bromine in (b), and 3 4 1 for chlorine and bromine in (c). If the numbers of halogens were not known, the pattern could be used in a reverse sense to decide their number. 

Laser isotope separation techniques have been demonstrated for many elements, including hydrogen, boron, carbon, nitrogen, oxygen, sHicon, sulfur, chlorine, titanium, selenium, bromine, molybdenum, barium, osmium, mercury, and some of the rare-earth elements. The most significant separation involves uranium, separating uranium-235 [15117-96-1], from uranium-238 [7440-61-1], (see Uranium and uranium compounds). The... 

Bromine [7726-95-6] Bi2, is the only nonmetallic element that is aUquid at standard conditions. Bromine [10097-32-2] Br, has at no. 35, at wt 79.904, and belongs to Group 17 (VIIA) of the Periodic Table, the halogens. Its electronic configuration is. The element s known isotopes... 

The distribution of a-bromoketones formed in the reaction of acetylcyclopentane with bromine was studied as a function of deuterium substitution. On the basis of the data given below, calculate the primaiy kinetic isotope effect for enolization of... 

Bromination has been shown not to exhibit a primary kinetic isotope effect in the case of benzene, bromobenzene, toluene, or methoxybenzene. There are several examples of substrates which do show significant isotope effects, including substituted anisoles, JV,iV-dimethylanilines, and 1,3,5-trialkylbenzenes. The observation of isotope effects in highly substituted systems seems to be the result of steric factors that can operate in two ways. There may be resistance to the bromine taking up a position coplanar with adjacent substituents in the aromatization step. This would favor return of the ff-complex to reactants. In addition, the steric bulk of several substituents may hinder solvent or other base from assisting in the proton removal. Either factor would allow deprotonation to become rate-controlling. 

Other mechanisms must also operate, however, to account tor the fact that 5-10% of the product is formed with retained configuration at the chiral center. Isotopic labeling studies have also demonstrated that the 3-bromo-2-butyl radical undergoes reversible loss of bromine atom to give 2-butene at a rate which is competitive with that of the bromination reaction ... 

Bromine is a red-orange liquid with an average atomic mass of 79.90 amu. Its name is derived from the Greek word bromos (fipofios), which means stench. It has two naturally occurring isotopes Br-79 (78.92 amu) and Br-81 (80.92 amu). What is the abundance of the heavier isotope ... 

When a uranium-235 atom undergoes fission, it splits into two unequal fragments and a number of neutrons and beta particles. The fission process is complicated by the fact that different uranium-235 atoms split up in many different ways. For example, while one atom of 292U is splitting to give isotopes of rubidium (Z = 37) and cesium (Z = 55), another may break up to give isotopes of bromine (Z = 35) and lanthanum (Z = 57), while still another atom yields isotopes of zinc (Z = 30) and samarium (Z = 62) ... 

Look for characteristic isotopic abundances that show the presence of bromine, chlorine, sulfur, silicon, and so on. If the deduced molecular ion is of sufficient intensity, the probable molecular formula may be determined using the observed isotopic abundances of the molecular ion region. Set the deduced molecular ion, M, at 100% abundance, and then calculate the relative abundances of M + 1 and M + 2 either manually or using the data system. 

The presence of chlorine and/or bromine is easily detected by their characteristic isotopic patterns (see Appendix 11). As in many aliphatic compounds, the abundance of the molecular ion decreases as the size of the R group increases. For example, in the El mass spectra of methyl chloride and ethyl chloride, the molecular ion intensities are high, whereas in compounds with larger R groups such as butyl chloride, the molecular ion peak is relatively small or nonexistent. 

Christen and Zollinger303 have made an extensive study of kinetic isotope effects in bromination of the disodium salt of 2-naphthol-6,8-disulphonic acid with hypobromous acid and with bromine in aqueous buffers at 20 °C. Both bro-minating agents give the same rate (within 20 %) and the reactions are first-order... 

A kinetic isotope effect, kH/kD = 1.4, has been observed in the bromination of 3-bromo-l,2,4,5-tetramethylbenzene and its 6-deuterated isomer by bromine in nitromethane at 30 °C, and this has been attributed to steric hindrance to the electrophile causing kLx to become significant relative to k 2 (see p. 8)268. A more extensive subsequent investigation304 of the isotope effects obtained for reaction in acetic acid and in nitromethane (in parentheses) revealed the following values mesitylene, 1.1 pentamethylbenzene 1.2 3-methoxy-1,2,4,5-tetramethyl-benzene 1.5 5-t-butyl-1,2,3-trimethylbenzene 1.6 (2.7) 3-bromo-1,2,4,5-tetra-methylbenzene 1.4 and for 1,3,5-tri-f-butylbenzene in acetic acid-dioxan, with silver ion catalyst, kH/kD = 3.6. All of these isotope effects are obtained with hindered compounds, and the larger the steric hindrance, the greater the isotope... 

Variation of the isotope effect with bromide ion concentration has also been observed for the bromination of 4-methoxybenzenesulphonic acid and its ortho dideuterated derivative at 0 °C, the value of kH/kD changing from 1.0 with no Br to 1.31 at 2.0 M Br" 308. 

The bromination of phenol in acetic acid, containing lithium bromide and perchlorate at a constant total concentration of 0.2 M, gave kinetic isotope effects... 

E.35 A mass spectrum of Br2 has three peaks, with the mass numbers 158, 160, and 162. (a) Use this information to determine which isotopes of bromine occur in nature, (b) If the relative heights of the peaks, which depend on abundance, are 33.8, 33.3. and 32.9. respectively, which isotope is more abundant ... 

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